VST looks at the Leo Triplet -- and beyond

July 27, 2011

Triplet of bright galaxies in the constellation of Leo (The Lion), together with a multitude of fainter objects: distant background galaxies and much closer Milky Way stars. The image hints at the power of the VST and OmegaCAM for surveying the extragalactic Universe and for mapping the low brightness objects of the galactic halo. This image is a composite created by combining exposures taken through three different filters. Light that passed through a near-infrared filter was coloured red, light in the red part of the spectrum is coloured green, and green light is coloured magenta. Credit: ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute

(PhysOrg.com) -- A huge image, from the new VLT Survey Telescope (VST) and its camera OmegaCAM at ESO's Paranal Observatory, shows a triplet of bright galaxies in the constellation of Leo (The Lion). But the faint objects in the background, rather than the foreground galaxies, are what may capture an astronomers attention. The VSTs sharp view of these dim objects hints at the power of the telescope and OmegaCAM for mapping the distant Universe.

The VST is the newest addition to ESOs Paranal Observatory. It is a state-of-the-art 2.6-metre telescope, which is equipped with a giant 268-megapixel camera, OmegaCAM. As the name indicates, the VST is dedicated to surveying the skies in visible light, and it is the largest telescope in the world designed exclusively for this purpose. This large view of the Leo Triplet demonstrates the excellent quality of images produced by the VST and its camera.

The Leo Triplet is a magnificent group of interacting galaxies about 35 million light-years from Earth. All three of them are spirals like our own Milky Way galaxy, even though this may not be immediately obvious in this image because their discs are tilted at different angles to our line of sight. NGC 3628, at the left of the frame, is seen edge-on, with thick dust lanes along the plane of the galaxy. The Messier objects M 65 (upper right) and M 66 (lower right), on the other hand, are inclined enough to make their spiral arms visible.

Large telescopes can normally study only one of these galaxies at a time, but the VST field of view  twice as broad as the full Moon  is wide enough to frame all three members of the group in a single picture. The VST also brings to light large numbers of fainter and more distant galaxies, seen as smudges in the background of this image.

In the foreground of the new image many point-like stars of varied brightness, lying in our own galaxy, can also be seen. One of the science goals of the VST is to search for much fainter objects in the Milky Way, such as brown dwarf stars, planets, neutron stars and black holes. These are thought to permeate the halo of our galaxy but are often too dim to be detected directly even by large telescopes. The VST will look for subtle events, produced by a phenomenon called microlensing, to detect these very elusive objects indirectly and study the galactic halo.

Through these studies, the VST is expected to further our understanding of dark matter, which is thought to be the largest constituent of the galactic halo. Clues on the nature of this substance, as well as on the nature of dark energy, are also expected to be found through the VSTs surveys of the distant Universe. The telescope will discover distant galaxy clusters and high-redshift quasars that will help astronomers understand the early Universe and find answers to long-standing questions in cosmology.

Very much closer to home, this image also contains the tracks of several asteroids within the Solar System that have moved across the images during the exposures. These show up as short coloured lines and at least ten can be seen in this picture. As Leo is a zodiacal constellation, lying in the plane of the Solar System, the number of asteroids is particularly high.

This image is a composite created by combining exposures taken through three different filters. Light that passed through a near-infrared filter was coloured red, light in the red part of the spectrum is coloured green, and green light is coloured magenta.

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"Can someone point out an asteroid or two? I can't seem to spot them anywheres."

The asteroid tracks appear as green or magenta-red pairs of tracks in the image, but to really see most of them(they are rather small and faint in this reproduction), check out one of the larger images at the ESO site: http://www.eso.or...126a.jpg

Three magenta-red pairs are probably the brightest here:

1-to the right of the galaxy at bottom left(NGC 3628)2-left of the galaxy at bottom right, in a faint extension of the galaxy(M 66)3-to the lower left of the galaxy at top(M 65)

-All 3 are faintly visible in the reproduction above(enlarged, natch) and the rest can be seen in the linked image. Happy hunting LKD!

"Why do they have dual colors denoting their traversing? Is this because of rotation?"

The red-magenta trails are the result of two exposures taken in sequence on the same night, but using different filters for each exposure. The greens trails represent a single exposure taken on a different night (and using a different filter than that used for the first two exposures).

Also note the colors here are only meant to be representative of the 3 filters used.

I've since downloaded a monster 260Mb version of the image, in part to look for additional trails (I'm up to 12 and counting....). A larger image still (over 480Mb) is available at the ESO website: http://www.eso.or...so1126a/

I've since downloaded a monster 260Mb version of the image, in part to look for additional trails (I'm up to 12 and counting....). A larger image still (over 480Mb) is available at the ESO website: http://www.eso.or...so1126a/

Why does there appear to be an upper limit on the mass/size of a galaxy? Is there a mathematical limitation of scale?

Could gravitational attraction to the center of mass be so tenuous at the outskirts as to become vanishingly small?

Or conversely, could too much mass/density cause a "crunch" into the central black hole?

Mass distribution due to the expansion of space certainly may play a role, but it seems clumpiness should be more apparent.

Another way to put it: What mechanism led to the distribution of mass we see today? Why was it diffuse enough to limit galaxy size, but not so diffuse as to prevent these structures from occurring to begin with?

"Why does there appear to be an upper limit on the mass/size of a galaxy?"

It is likely that this is in someway related to the well-known M-sigma relation found for many galaxies harboring a SMBH: http://en.wikiped...relation

Some sort of feedback mechanism seems to exist between the SMBH and the stellar environment (kinematics, composition, mass evolution) found in the outskirts of the disk and thin halo. The kinematics and evolution of the outer portions of these galaxies can have a profound effect on the final configuration of the galaxy.

Another way to put it: What mechanism led to the distribution of mass we see today? Why was it diffuse enough to limit galaxy size, but not so diffuse as to prevent these structures from occurring to begin with?

Enter the questionable Dark matter. It's quite a touchy subject...

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